My primary research objective is to describe the sequence of metabolic reactions which lead to the secretion of hydrochloric acid by the gastric mucosa and to identify those reactions which serve as the major controlling steps in this process. My approach to this problem relies primarily on the recent development of non-destructive optical techniques which permit the monitoring of certain intracellular reactions in the intact tissues. Methods are presently available for monitoring oxidative metabolism and intracellular pH changes. These techniques are used in conjunction with more conventional measurements of oxygen utilization and metabolic intermediates to characterize the time relations between various reactions as a means of identifying the controlling steps in acid secretion.